We tested for total coliforms and for other bacteria, including enterococcus, that are better indicators of fecal contamination. Federal action limits exist for indicator organisms in water, raw meat, milk, and some processed foods, but not produce. Those organisms are typically used to gauge possible pathogen contamination.

Several industry experts we consulted suggested that for leafy greens, an unacceptable level of total coliforms or enterococcus is 10,000 or more colony forming units per gram (CFU/g) or a comparable estimate. In our tests, 39 percent of samples exceeded that level for total coliforms and 23 percent for enterococcus.

According to the report, "[w]hether the greens came in a clamshell or bag, included 'baby' greens, or were organic made no difference." Nor is contamination limited to off-brands; in fact, "brands for which we had more than four samples, including national brands Dole, Earthbound Farm Organic, and Fresh Express, plus regional and store brands, had at least one package with relatively high levels of total coliforms or enterococcus."